Method of making heat-exchange cores



3 Sheets-Sheet 1 P. R. SEI-:MILLER METHOD' oF MAKING HEAT-EXCHANGE czoREsl Filed oct. 1s, 1939 Aug. 12, 1941.

ATTORNEY 5 AU8- 121 1941- P. R. sEMlLLl-:R 2,252,210

METHOD OF MAKING HEAT-EXCHANGE CORES A Filed 001;. 18, 1939 3 She-etS-Sheet 2 PaaLSQ@ 72am?? Patented Aug. 121941 METHOD F MAKING HEAT-EXCHANGE I COBES Paul R. Seemiller, Detroit, Mich., assignor to McCord Radiator & Mfg. Co., Detroit, Mich., a corporation of Maine Application October 18, 1939, Serial No. 299,954

7 Claims. .(Cl. 113-118) This invention relates to method of making a heat exchange core. It primarily concerns a tubular type radiator core for use with internal combustion engines such as those used in motor vehicles and airplanes but it may also be used in other heat exchange devices.

The general object of the invention is to provide an improved tubular heat exchange core.

Another object is to provide an improved process for making tubular heat exchange cores.

Other objects and advantages of the invention will appear from the following specification' and the drawings.

An embodiment of the invention is shown in the accompanying drawings in which:

Figure 1 is a perspective View of one of the heat exchange elements or fin Sections used in the core.

Fig. 2 is a perspective view of one of the tubes employed in the core.

Fig. 3 is an enlarged end viewof the tube shown in Fig. 2.

Fig. 4 is a perspective view showing how the iin sections and tubes are assembled to make the core.

Fig. 5 is a partial, longitudinal cross section of a portion of a completed core showing how the n sections and tubes are united.

Fig. 6 is a partial cross section at right angles to that of Fig. 5 showing how the n sections and tubes are united.

Fig. 7 is a partial perspective of a portion of the standard type of tubular radiator core.

Fig. 8 is an enlarged partial end view of the core of Fig. '7.

Fig. 9 is a front elevation of a completed core, the view being broken along both vertical and horizontal lines so that it will not occupy so much space.

Fig. 10 -is an end view of the completed core of Fig. 9, said view being broken along a horizontal line.

Fig. 11 is a top view of the completed core, said view also being broken along a horizontal line.

Fig. 12 is a partial perspective of one of the head pieces of a radiator. u l Y .'Fig. 13 is a.- front sectional elevation of a completed core showing it mounted in Vhead plates and as it appears in a finishedv radiator, the view being broken along a horizontal line. x

Fig-14 is aperspective view of an apparatus in which the core may be assembled, some of the `core parts beingillustrated yin assembled relation. l. 1 Fig. 15 is an end view of the apparatus shown inFig.,1 4. l,

Fig. 16 is a top plan view of said apparatus.

Fig. 1 7 is a side view of the apparatus of Fig. 14 with two completed cores in it.

Fig. 18 is a vertical cross section of a furnace in which the apparatus with the assembled radiator cores in it may be placed for performing one of the steps in the process of making said cores.

The present invention is a continuation-inpart of prior application, Serial No. 280,133, filed June 20, 1939.

The invention can be more clearly vexplained by first outlining the problems involved in radiator core construction and manufacture so that their solution by the present invention will be understood.

The two types of automotive radiator cores in general use are the cellular and the tubular types. The cellular type has been predominant because of the ease and cheapness of assembly as well as better cooling capacity in a restricted space and more cooling capacity per pound of metal used. On the other hand, the cellular type has certain disadvantages in that the water passages are not as free, as straight, or of as large a size as desirable; the structural strength is not great; and it has a multiplicity of overlapping seams that are sealed only by solder, the latter condition being increasingly detrimental owing to the presentday tendency of allowing a small pressure to develop in the cooling systems of automobiles.

The'tubular type has certain well-recognized advantages such as straight and unobstructed water passages of adequate size formed by the tubes; greater structural strength; and no lapped seams that are sealed only by solder. However, owing to the nature of its construction and the manner in which it has had to be assembled, the cost of the tubular type has been such as to offset, to a great extent, its advantages.

vThe characteristics desired in a tubular heat exchangehcore are a maximum cooling capacity per cubic inch of core so as to get the required cooling action in a minimum space; the maximum cooling action per pound of metal used to thereby keep the cost low because the materials employed,.such,as copper, brass, and solder, are

struction that can be easily and effectively serviced; together with which there must be the requisite structural strength, flexibility, and pleasing appearance.

The present invention achieves these results and, in fact, retains the advantages of the tubular type of core while, at the same time, obtaining the advantages of the cellular type.

Present-day tubular radiators are made by pushing tubes I (Fig. 7) through openings in individual fins 2 of which there are usually a large number as shown in Fig. 7. The fins 2 are stamped out of copper or brass that must be relatively hard and stii in order that the tubes may be pushed through the openings in the flns.

This requires the use of what is known as a silver-bearing copper of which there is only a limited supply and which is relatively expensive. A multitude of slot-like openings 3 are punched in the fins which requires expensive dies that wear quite quickly and that require constant attention. In punching these holes, the metal is drawn out to form a short ange 4 (Fig. '1)l at right angles to the surface of the fin, but these flanges are invariably ruptured at bothA ends of the slot as illustrated in Fig. 7 because of the hard nature of the copper that must be employed to make the fins stiil. Thus, the flanges are very imperfect. After the fins have been stamped and punched, they must be assembled and held in proper spaced relation which requires a special jig or xture in which the fins must be carefully assembled. The tubes! are then pushed one at a time through the openings in the assembled group of ns. The tubes must be quite stiff to prevent bending but, even when made stiff, they mgust first be inserted through an arbor which is put 4against the opening in the first n and the tube pushed through the arbor and then carefully pushed on through the openings in all the fins, the arbor being necessary to prevent bending of the tubes. It has been found from experience that, in order to reduce the fin and tube deformation to the lowest practical value, the ns must be made of hard copper of at least four thousandths of anv inch (.004") thickness and the tube walls must be atleast six thousandths of an inch (.006"). Even with these thicknesses, it is necessary, after the core has been completed, to carefully go lover it to see that'the fins are properly spaced apart and that they have not been deformed in the assembly process. The above process is a slow, tedious and costly one that must be performed by skilled operators. Even with the best materials available and'with skilled operators, there is a marke-d wastage of tubes, fins, and partly assembled cores. The efliciency of a core of this type depends largely upon the metal-to-metal contact between the tubes andthe fins because the heat from the water in the tubes must pass through the tube walls to the fins so that it may be dissipated by the air going past said flns. In the construction just described, themetal-toinetal contact is very poor and haphazard. In the first place, the dies for punching the holes wear rapidly and to different extents so that some of the holes are soon slightly larger than others. The tubes l do not always come of uniform size nor of the same size throughout, and the thickness of the metal employed in them may vary slightly. Also, the tubes may be bent or twisted slightly either before or during the assemlbly. Then, too, the holes in the fins must be appreciably larger than the tubes in order that the tubes can be pushed through the fin assembly. Because of these conditions there is often a space between the edges of the openings in the iins and the tubes, which space may vary and is difficult, if not impossible, to control. This condition is illustrated in Fig. 8 by the space 5, the actual dimensions being somewhat exaggerated in order that the lines of the drawing may not run together. After the core is assemble-d, the tubes are soldered to the ns but, at the time this occurs, the core is in assembled condition and there is no way of getting at the openings except on the two outside ns. 'I'he result is that the soldering is very uncertain and, because of the varying space between the tubes and the edges of the openings, the soldering may be only in spots 6 as illustrated in Fig. '1. There is no way of correcting this difliculty in the assembled core, as the interior of the core `is inaccessible. The metal-to-metal contact in'a core of this type is so uncertain that cores of the same size vary in cooling capacity by as much as four per cent. From all of this it will be clear that the standard type' of tubular core is not only expensive but it is also of uncertain efliciency. These factors have worked against the use of the tubular type of core as compared with the "cellular type.

The present invention departs radically from the usual practice in making tubular cores. Instead of using a multiplicity of independent fins, the heat dissipating elements are made in integral sections, such as the section I0 shown in Fig. 1. 'Ihese sections will be called the "fin sections for convenience in description. Each fin section is made of an integral strip of soft metal, preferably soft, pliable copper, which has a Width in the direction A of Fig. l equal to the thickness of the radiator core and a length B, preferably substantially equal to the height of said core (Fig. 13).

The metal strip I0 is reversely folded, or accordion-pleated, as shown in Fig. 1, to form a multiplicity of folds Il that are substantially parallel to one another and relatively close together. The frequency of the folds is usually about ten per inch, that is, there are ten thin metal strips Il per lineal inch of completed fln section. This frequency may be variedto suit the requirements but is preferably kept between nine and twelve folds per inch. The bends in the metal are approximately degree bends so that the folds are approximately parallel to each other but itis to be noted that there is a substantial curve at the bends or edges of the folds as illustrated at I2 in Fig. 1 so as to provide a substantial surface along the tops of the bends for purposes that will presently appear. The copper employed need not be a silver-bearing copper but may be a soft copper that is less expensive.l Also, the metal employed is thinner than that which can be safely used in the oldv style tubular construction. For example, copper three thousandths of an inch (.003") thick can be easily and safely used, whereas the fins in the old construction must be at least four thousandths (.004) thick. While this is not a. great dierence' in actual fractions of an inch,vrelatively it is a big difference and results in a marked economy in the use of an expensive metal, as will be explained later. The thickness of the completed iin section in the direction C in Fig. 1 is preferably approidm'ately seven sixteenths of an inch soft copper is obtained by having the folds paral- 1el, the edges roundedV and by having a multiplicity of folds per inch.

The fin section vis preferably formed with 'humps `or projections I3 in the individual folds,

which humps may also be considered indentations depending upon which side of the fold is being considered. It is to be noted that these humps are obtained without cutting or breaking the metal, the fin foldsv being imperforate. Because of the soft metal used, these humps may be made higher, or of more substantial depth, than is pos sible in the old hard copper fins, and the result-I ing air surface of the ns can thus be increased for -a given dimension of fin section. The humps are about three thirty-seconds of an inch deepand they are in the form of truncated pyramids which not only alternate indirection relative to the surface of the fold from one end of the fold to the other but which also alternate as to height from the top or bottom of the fold. In other words, starting from the right-hand end 'of the first fold in Fig. 1, the first hump projects toward the reader and is tow-ard the top of the fin fold,

the next hump-projects away from the reader. Vand is toward the bottom of the fold, the next hump projects toward the Areader and is toward the top, and so on across the'length of the fold. In the completed section, these indentations or humps/in one fold register withthose ln the next vadjacent fold as shown' in Fig. 10. 'I'he result is that an air passage is provided between the individual folds of thev fin section which is undulating or sinuous in planes that are at right angles tov one another or, when the core is in vertical position, the air passage is undulating in both ahori- ,fr zontal and a vertic-al plane. This provides an im- `l proved air turbulence over prior constructions and this improved turbulence, together with the l creased size of the humps made possible by the i softfmetal. employed, increases the cooling 'ca- 'l pacity and efficiency of the iin section without intrffegi'ngwith proper air ow through the passage.

The yfin-section also may'h'ave a series of spacer humps la (Figs. 1,710 and 11) formed on it which are used in making the fin section, which tend to keep` the folds properly spaced after the fin vsection is completed,and which increase the air surface slightly.

The tubes I6, shown in Figs. 2 and 3, are made of copper or brass and, because these tubes do not have to be pushed through openings' in iins as, will presently appear, it has been found that the `tube wall thickness can be reduced by sixteen per cent as compared wlththe old construction and that a tube wall thickness of five thousandths of an inch (.005") gives as good a performance as Y. was previously' obtained Witha tube wall thickness of six thousandths of an inch .006)'. -Fur- ,.'thermora variations in size or in the straightness The tubes are substantially fiat though slightly bulged along the longitudinal center as shown in Figs. 2 and 3. They are formed with lock seams v such as shown' at I'I, and these lock seams are preferably located along the side edges of the tubes. The lock seams extend for the full thickness of the tubes to provide four thicknesses of i metal on edge and an important feature is that these lock seams are accurately made to act as spacers for determining the final thickness of the vtubes in the completed fcore. The dimensions of the lock seams in the ldirection of the thickness of the tubes vare kept to within four thousand'ths of aninch. The lock seams also stiien the` tubes and prevent their collapse during assembly of the core by acting as stops or spacers preventing the fin sections from compressing the tubes beyond acertain limit. l

'Ihe tubes are formed in a tube mill, which has not been shownw because it is of a well known type, l

by a continuousprocess thatbends a strip of sheet metal to shape and forms a lock seam in it. In the present invention, the tube mill is adjusted to give a lock seam of -accurate dimensions and of'the type shown and described. During the making of the tube, the llock seam is soldered and, while this is being done, the entire outside of the tube is covered with a thin coat of solder i core is to provide water passages and it will be ,observed that they provide straight, smooth, un-

obstructed passages that cannot beeasily clogged by rust or other foreign material. Furthermore,

.l the passages are devoid of lapped or soldered joints such as would easily leak under severe service conditions. y vided which will notv leak under severe'service conditions including considerable pressure.

Instead a lock seamhas been pro- After the tubes and fin sections, have been formed, the process of making the core starts with one 'of the nn sections III `shown in Fig. -1.

Referring to Fig. 4, one of these fln sections is placed in position and then a set of tubes `I 6 having solder and `flux on their Voutside surfaces is v,placed on top of the n section inproper spaced relation Four tubes comprisefa set in thecore `illustrated in Fig. 4. yIt is to be noted thatfthe substantially nat, lower sides of the tubes vrest on the edges I2 of the folds of the iin section so as ,to contact all of the top edges of the nyfolds 60T' Next, another fin section is placed on top of the for the width of the core. v

set of tubes and, as will be clear fromlFig. 4, the

top 1 of the-set of'tubes contacts allthe lower edgesA of the folds-of the second fin section.

Then a secondset' of tubes is placed on top `of the second fin section; a third iin section is l placed in'position, a'third seti of tubes is placed on top of the third fln'section,-l and these 'steps arecontinueduntil the radiator core is off-the desiredsize. I w

, The; assembled fin sections-and' tubesarek then forced tightly together and clamped to holdthe parts. rmlyin position and to obtain complete and definite contact between each tube and all thel edgesof the -nsections adjacent. it. vThe tion also tends to keep them in good contact `with the fin sections.v This flattening of the tubesy does not deform their inner surfaces. They still have 'ample' capacity and provide smooth unobstructed passages. The lock seams on the sides of the tubes provide four spacers between each two iin sections which accurately space the iin sections and which prevent collapse of the tubes. The soft copper out of which the fin sections are made may allow some of the edges of the folds to yield slightly should some of the edges be slightly higher than others, although, as a whole, these fin sections are very resistant to pressure owing to the construction of the iin elements with the folds substantially parallel and close together and the bends rounded. 'I'he iin sections thus space the sets of tubes and the tubes space the fin sections, with the result that the sets of tubes are accurately spaced to enable them to enter the holes in the headers later described. 'I'his spacing must be within several thousandths of an inch but by using accurate lock seams and by means of the type of nn section employed, it has been found that this accurate spacing of the tubes can be obtained.

Whilethe core elements are thus held tightly together in proper relation to each other, the assembly is subjected to heat suiilcient to cause the solder on the tubes to soften and flow enough to solder the tubes to the fin sections.

Immediately afterward, the unit is either cooled or quenched or allowed to cool in the atmosphere to thereby solidify the solder, the parts being held firmly in position by the clamps until the solder has solidied.

The process also results in integrally bonding or uniting all the folds ofr each iin section to the respective tubes engaged by it, that is, to the sets of tubes on each side of it; and this uniting or bonding is not only a definite and uniform one for each and every fold, but it is a uniting that occurs for the full width of each tube along a band of substantial width owing to the substantial width of the bends of the folds in the fln sections.

'I'he resulting construction is shown in one cross section in Fig. 5 and in another cross section in Fig. 6, where, however, the relative amount of solder between the iin edges and the tubes has been exaggerated to avoid having the lines of the drawing run together. In actual practice the amount of solder is kept at a minimum in order to obtain as nearly as possible a metal-to-metal contact between the copper fln'edges and the brass tubes, copper and brass being better heat conductors than solder. Figs. 5 and 6 show how the fins are made an integral part of the tubes and hcw they are united along a line of substantial width and for the full width of each tube. It is to be observed that the soldering takes place along the edges oi the n folds only, as distinguished from constructions that are dipped, where the entire iin section is covered with solder. Such constructions are not only wasteful of solder but are not as efficient because the solder on the n sections detracts from the efficiency of said sections as heat conductors.

This method of making a. radiator core is much simpler and a great deal less expensive than the constructions heretofore used in which the tubes are pushed through individual fins. The assembly operations that have been wasteful of time and material have been eliminated. The new assembly operations are few and very easy. The number of parts in a radiator of a given size and capacity is reduced approximately one third. Moreover, the contact between the tubes and the iins is much greater and much better, and there is no uncertainty about it. Even though the tubes may vary slightly in size and even though the folds of the iin section may vary slightly at places or be slightly bent or twisted, nevertheless, this type of construction and method of assembly are such that, when the parts are clamped together, the tubes will yield slightly and flatten out to give complete and definite contact between each fold of each iin section and each of the tubes that it is supposed to contact and, after the soldering action, every fold is intimately united to its tube throughout the entire surface of contact; and this is not a contact along a sharp edge but a substantial contact over a folded edge of substantial width and for the full width of the tube.

The lock seams on the side edges of the tubes provide four accurate spacers between each two iin sections and prevent collapse of the tubes. The nature of the in sections is such that, even though they are made of soft copper, they accurately space the tubes and they act as a firm Vbracing means between the tubes to give the core excellent structural strength.

One of the most important advantages is that the thickness of the metal in the fln sections and the tubes may be reduced without in any way reducing the heat dissipating capacity of the core or interfering with its assembly. It has been found that, for cores of a given heat dissipating capacity, the amount of metal per nished core isreduced by five pounds, or about twenty-iive percent, as compared withthe standard tubular construction. Thus, a much greater efficiency per pound of metal used is obtained. Since the metal is expensive, this results in a very substantial saving when it is considered that thousands of these cores are made per day. There is, of course, also a commensurate saving in the simplicity and ease of assembly. It has'also been found that only about one-third (l) as much solder is used as compared with the standard cellular type. This is a great economy in tin which is one of the main ingredients of solder andwhich has to be imported into this country.

Another advantage is that there is no damaging, and consequent scrapping, of valuable metal during the assembly. As stated, in the old con? struction, even when the utmost care was used by trained operators, there was a considerable percentage of damaged fins, tubes and partly assembled cores.

The method of making the core is illustrated in further detail in Figs. 14 to 18, where an apparatus that may be employed in the assembly operation is shown.

In this form of apparatus, the core parts are assembled in a rectangular box-like xture 20 mounted on rollers 2| that enable it to be easily moved about. Before thel parts are asserbled in this frame, it is preferably tilted to a slightly inclined position against a support 22 as shown in Fig. 15 in order that the fin sections, as they are placed in the frame, will fall easily into correct position against the back of the frame. The

inner edges of the ends 23 oi the frame are provided with grooves 24 to receive the ends of the tubes I8 and to hold said tubes in proper spaced relation. l

The operator starts by placing one of the iin sections I0 in the bottom of the frame and -pushing said section tightly against therear of the frame as shown in Fig. 14, if the .section does not fall into correct position automatically,

'I'hese 1in sections are cut accurately to proper length .and normally iit nicely between the ends of the fixture but, if any iin section has been elongated slightly,it can nevertheless be placed in the fixture in which event it may bulge up slightly but the set of tubes that is placed on top of it will push it down to position.

The operator then puts a set of tubes I6v into the grooves 24 and allows them to drop down into position on top of the fin section l0. Another fin section is then placed in position, an-

other set of tubes is inserted, and this continues until the core is of the desired height or size.

Next, the assembly is clamped together by any suitable means, a two-piececlamp being used in the apparatus shown. This clamp has a lower piece 25 and an upper piece 28. The lower piece 25 has spaced, bent-over ends that project into openings 21 (Fig. 14) in ahead -piece 28 which may be fixed to the frame 2li, or loose, as desired. The upper end 26 of the clamp projects over another head piece 29 (Fig. 1'?)v and the two parts of the clamp are drawn together by a hand lever 30 which is journaled in a tongue on the upper piece 26 of the clamp and which has eccentric cams 3| (Fig. 15) flxedto it that engage shoulders on the upper end of the lower -part 25 of the clamp. A short turnY of the handle 3|) brings the two parts of the clamp together, the parts 25, 26, together with the cams 3|, being proportioned so as to force the core elements together with the required degree of pressure, which may be varied to some extent by the operator who soon learns the correct degree of pressure to be applied to the handle to hold'the parts together in the proper manner.

In the apparatus illustrated, two cores are assembled at the same time in frame 20. In that event the second core is assembled on top of the `head piece 29 and a third head piece 32 isem- After the cores have been assembled ,and l clamped together, the frame, together with the cores in it, is rolled into an oven- I0 where heat is applied bymeans of a hot air heating apparatus 4I. The temperature is regulated so that the solder. islsoftened justenough to enable it to flow for purposes of uniting the tubes and the fins, after which the apparatus is rolled outof the furnace and the core is either-cooled `or allowed to cool. The heating and cooling operation ispreferably a continuous one vinwhichthe assembly is slowly moved into, through, and out of a furnace with the temperature and time elements regulated to get the correct soldering action.

After the core has cooled, the ends 23 of the frame may be swung outward as shown in Fig. 17. the cores removed, and the clamps loosened.

While the above apparatus has been found to work very satisfactorily, the practice of the process does not depend upon this particular form of apparatus.

4 After the core has-been completed, the ends of the tubes which project from thebottom and top of the core are inserted in head sheets 50.

. as shown in Fig. 13. These head sheets, a portion of one of which is"illustrated in detail in Fig. 12, have'openings 5I punched in themto receive the tubes. During the punching operation the metalis drawn out into ilanges 52. These openings are provided with considerable lead at their ends Aand side edges, as shown at 53 in Fig. 12, so that, if any of the tubes in the flnished core should be slightly out of line, the head sheet can nevertheless, be easily pushed on the ends of the core. After the head sheets are placed in position, the parts are heldv together and the assembly is heated at its ends only. This results in soldering thek en'ds of the tubes to the head pieces by means of the solder on the outsides of the tubes and it also softens the solder a few inches back-from the top and bottom of the core to allow any `tubes thatmay be slightly out of line to adjust themselves so that there will be no `strain on the core.

It is to be understood that the radiator core construction and method of making thev same disclosed herein are for purposes of illustration only and that variations may be made within the spirit and scope of the invention as defined by the appended claims. 1

1. The method of making a heat-exchange core of the tubular type which comprises forming a thin, flat, metal tube with a lock seam on its side edge accurately made to act as Va spacing means for the thickness of the tube; cutting said tube into predetermined lengths; forming pleated iin sections out of softl metal with folds substantially parallel with'one another" and with the folds of' a frequencyv sumcient to give said sections rigidity in the direction of their thickness; assembling said fin sections and sets of said tubes in contact with one another, with the sections and sets of 4tubes alternating and with the folds of said fin sections substantially lat right angles to the planes of said tubes; forcing said assembled n sections and tubes tof gether under pressure, with said lock seams acting to space said iin sections and saidnn sections acting to space said sets of tubes, to thereby bring said iin sections and tubes into intimatev engagement, with the sets of tubes in accurate spaced relation;l and uniting said fin sectionsand tubes while they are so held.

2. The method of, making a heat vexchange core of the tubular type which comprises.v assembling a plurality o f pleated metal iin sections each having a multiplicity of folds that give the section rigidity in the direction of its thickness, in

contact on the edges lof their folds with ia plu,-vv

rality of thin `iiat metal tubes having opposite convex iin engaging sides, the fin Vsections andr sets of tubes alternating with the folds of the hn. sections at right angles to the tubes, forcing said` assembled fin` sections and tubesy togetherunder suiiicient pressure to compress'the convex portions of said tubes until the opposite sides of the tubes are substantially parallel and insure contact between the tubes and the'folds of the fin sections, and uniting said fin sections and tubes while they areheld in said engagement.

3. 'I'he method of making aheat-exchange core of thetubular type which comprises formmg a thin, nat tube with a lock seam on its side edge accurately made to act as a spacing means equal to the final thickness of said tube in the core; soldering said lock seam and applying a coating solder and a soldering flux to the outside of said tube; cutting said tube into predetermined lengths; forming pleated metal iin sections out of soft metal with the folds substantially parallel, with the edgesof the folds rounded and of substantial width, and with said folds of sufficient frequency to give said n sections rigidity in the direction of their thickness; assembling sets of said tubes in contact with the edges of the folds of said fln sections with the sets of tubes and fin sections alternating and with said folds substantially at right angles to the planes of said tubes; forcing said assembled fin sections and tubes together under pressure, with said lock seams acting to space the fln sections and said fin sections acting to space said tubes, to thereby bring said-nn sections and tubes into intimate engagement, with the sets of tubes accurately spaced from one another; applying heat to said fin sections and tubes while they are held in said engagement to melt the solder on the outside of said tubes; and -cooling said fin sections and tubes while held in said engagement to thereby produce a core with the tubes and fin sections integrally bonded together.

4. The method of making a heat-exchange core of the tubular type which comprises assembling a plurality of pleated metal fin sections each having a multiplicity of substantially parallel folds that give the section rigidity in the di rection of its thickness, in contact on the edges of their folds with a plurality of thin, nat, metal Vtubes that are slightly bulged along their longitudinal center lines and have means on them forming an accurate spacing means equal to the final thickness of the tubes in the core, the fin sections and sets of tubes alternating; forcing said assembled n sections and tubes together under pressure to iiatten said tubes until said spacing means acts to space said fln sections and said n sections acting to space said sets of tubes, to thereby bring said iin sections and tubes into intimate engagement, with the sets of tubes accurately spaced from one another; and uniting said fin sections and tubes while they are held in said engagement.

5. The method of making a heat-exchange core of the tubular type which comprisesv forming a thin, fiat tube with a slight bulge along its llongitudinal center line and with a means on it ing said assembled iin sections and tubes together under pressure to flatten said tubes until said spacing means acts to accurately space theV fin sections, to thereby bring said iin sections and :tubes into intimate engagement, with the sets of tubes accurately spaced from one another; and uniting said fin sections and tubes while they are so held together.

6. The method of making a heat-exchange core of the tubular type which comprises form-- ing a thin, iiat tube with a slight bulge along its longitudinal center line and with a stiffening means positioned to act as an accurate spacing means for the thickness of said tube; coating the outside of said tube with solder and a soldering flux, cutting said tube into predetermined lengths; forming pleated metal fin sections out of soft metal with the folds substantially parallel, with the edges of the folds rounded and of substantial width, and with said folds of suffi.- cient frequency to give said n sections rigidity in the direction of their thickness; assembling sets of said tubes in contact with the edges of the folds of said n sections with the sets of tubes and iin sections alternating; forcing said assembled fin sections and tubes together under pressure to atten said tubesI until said stiffening means acts to space the fin sections and said fin sections acting to space said tubes, to thereby bring said n sections and tubes into intimate engagement, with the sets of tubes accurately spaced from one another; applying heat to said fm sections and tubes while they are held in said engagement to melt the solder on the outside of said tubes; and cooling said fin sections and tubes while held in said engagement to thereby produce a core with the tubes and fin sections integrally bonded together.

7. The method of making a heat-exchange core of the tubular type which comprises ,forming a thin, flat metal tube with a slight bulge along its longitudinal center line and with a lock seam on its side edge accurately made to act as a spacing means for the thickness of the tube; soldering said lock seam and applying solder and a flux to the outside of said tube; cutting said tube into predetermined lengths; forming pleated iin sections out of soft metal with folds substantially parallel with one another and with the folds of a frequency suflicient to give the sections rigidity in the direction of their thickness; assembling said fin sections and sets of said tubes in contact with one another, with the fln`sections and sets of tubes alternating; forcing said assembled n sections and tubes together under pressure to iiatten said tubes until said lock seams act to space said fin sections and said fin sections acting to space said sets of tubes, to thereby bring said fin sections and tubes into intimate engagement, with the sets of tubes in accurate spaced relation;

applying heat to said iin sections and tubes to melt the solder on the outside of said tubes;-

and cooling said fin sections and tubes while they are held in engagement, to thereby produce a tubular core with the tubes and fin sections integrally bonded together.

' PAUL R. SEEMILLER. 

